1. Field of Invention
The present invention relates to the assembly of a Beam Splitting cube and to a Polarizing Beam Splitter (PBS) cube. The present invention includes tooling and procedures that allow the assembly of PBS in which the “pathlengths” of light through the PBS are matched. The present invention provides inexpensive methods and procedures to implement pathlength matched PBS construction in high volume manufacturing environments.
2. Discussion of Background
The concept of pathlength matching is illustrated in FIG. 1 (Path 1=Path 2) in a Beam Splitting Cube 100. Beam Splitting Cube 100 is constructed of 2 optical components, an upper prism 105 and a lower prism 110. The prisms 105 and 110 are joined at a common diagonal 115. The PBS 100 has 2 illustrated paths, path 1 from a Face 1 of prism 105 to a Reference face of prism 105, and, path 2 from a Face 2 of prism 110 to the Reference face of prism 105. The illustrated paths are physical pathlengths that are substantially equal (ideally, to be exactly equal, these paths would also be on top of each other on the horizontal portion of the paths through prism 105). Hence, optical pathlengths at a given wavelength along the same paths are also substantially equal. As noted above, commercial PBS's are not usually pathlength matched. This is due to the fact that most individual prisms are not produced to a high physical tolerance and that variations are not normally accommodated in the PBS assembly process. Next, note that there are applications that use various pathlengths through an optical assembly (a PBS being one example) be matched. One example of such an optical assembly is disclosed in the above-referenced patent application entitled “METHOD AND APPARATUS FOR CONFIGURATION AND ASSEMBLY OF A VIDEO PROJECTION LIGHT MANAGEMENT SYSTEM.” However, this and other optical assemblies generally require costly PBS production techniques.
In the past, two different methods have been used to produce pathlength matched PBS.
The first method is to measure the dimensions of all prism components and to sort them into groups having identical dimensions. Only prisms drawn from the same group would be mated. This method can produce a pathlength matched PBS but requires the additional labor associated with the measurements and provides additional opportunity to damage delicate prism surfaces. In addition, implementation of this method requires maintaining a substantial inventory of prism components to support high volume PBS manufacturing.
The second method is to measure the physical dimensions of the PBS during the assembly process. Then, the dimensions of the PBS are modified by adjusting a thickness of the glue line. The glue line is along the diagonal of the two prisms. In practice, this fabrication method is found to be slow, require considerable operator skill, and provides a poor yield.